1. Field of the Invention
The invention relates to imaging systems and more particularly to packaging for image sensing devices.
2. Description of Related Art
Image sensing devices generally are characterized as the light detecting component in digital imaging systems. An image sensing device in a camera, for example, uses light to capture an image so as to replace traditional film-based systems. In a camera, an image sensing device is configured to capture a monochrome or color image by way of field effect transistor (FET) or diode devices, fabricated with complementary metal oxide semiconductor (CMOS) devices or charge couple device (CCD) technology.
Imaging systems built with CCD or CMOS based sensors generally require an infrared (IR) selective filter as part of the optical system. This need arises because the most common semiconductor-based image sensing devices, silicon-based image sensing devices respond not only to visible light (approximately 380 to 780 nanometers), but also to infrared light in the range of approximately 780 to 1100 nanometers. Without an infrared blocking filter, it is virtually impossible to obtain a high-quality color image due to the combination of visible and IR signals. Monochrome imagers also require an IR selective filter to correctly preserve scene luminance.
Typically, digital imaging systems incorporate an IR filter, typically glass or plastic, as part of the optical train, i.e., somewhere in the optical system apart from the image sensing device and either overlying the lens or interposed within other optical elements. The disadvantage of the inclusion of a separate IR selective filter is that it adds an additional component to the total system count, i.e., piece-part count. The inclusion of an additional component must be accommodated thereby adding additional complexity to the imaging system. Further, depending on where the IR selective filter is placed, there is a size consideration that directly affects the cost of the imaging system. The system software and signal processing must also be adjusted to accommodate the color performance characteristics of the IR selective filter. Still further, if the IR selective filter is placed, for example, in front of the lens, the IR selective filter is exposed to the environment and therefore presents the risk of damage by the environment, such as for example moisture or scratching.